The present invention relates to a vacuum testing method and apparatus and more particularly to a method and apparatus for testing the integrity of fusible glass bulb sprinkler heads.
Various forms of automatic fire protection systems are presently available. Such systems generally include a plurality of automatic sprinkler heads. Each sprinkler head includes a body which defines a nozzle, a frame supporting a deflector and a cap or closure plug which seals the nozzle. A thermally responsive assembly is positioned between the frame and the cap. The assembly releases the cap when a predetermined ambient temperature is reached. Various forms of thermally responsive assemblies have been used in automatic sprinkler heads. These assemblies include mechanical, fusible links as well as fusible glass bulbs. The fusible glass bulbs, depending upon their size and temperature rating are partially or completely filled with a glycerin, water and alcohol solution or other suitable fluid. The fusible bulb includes an elongated, narrow extension or pip formed when the bulb is closed or sealed after filling. The filled bulb will include a "bubble". The size of the bubble decreases with an increase in the temperature rating. When the bulb is heated, the pressure within the bulb increases until it breaks or shatters. When the fusible bulb shatters, the cap or plug is released, thereby opening the nozzle and actuating the sprinkler head.
The glass bulbs are relatively delicate. Handling of the bulbs during shipment, packaging and assembly may result in damage to the bulb which would not be noticeable by an unaided visual inspection. The bulb may in fact be cracked or the pip may be broken. Although damaged, the bulb may retain the solution within it and appear to be operative. However, when the bulb is heated beyond its rated temperature, the fluid or liquid within the bulb will be forced out through the crack. The internal pressure within the bulb is thereby released and the bulb will not break or shatter. The automatic sprinkler head will fail to actuate when needed.
A need exists for a method and apparatus for testing fusible glass bulbs and automatic sprinkler heads incorporating fusible glass bulbs to determine the integrity of the glass bulb.